The invention relates to photoresist polymers and photoresist compositions including the polymers. In particular, the invention relates to polymers and photoresist compositions suitable for photolithography processing wherein the polymers include repeating units based on derivatives of Meldrum's acid (i.e., 2,2-dimethyl-1,3-dioxane-4,6-dione).
According to the International Technology Roadmap for Semiconductors (ITRS) 2006 Update, EUV lithography is the leading candidate for 32 nm half-pitch device manufacturing. Even though the current lack of progress in tool and resist availability has cast doubt on this assertion, EUV is still considered as one of the candidates for this generation of lithography. One of the concerns of EUV resists is outgassing, which can contaminate the optics when the resist is irradiated with highly energetic EUV radiation under vacuum. It has been demonstrated that EUV outgassing is higher than outgassing at 193 nm and 157 nm for a particular resist (W. D. Domke et al., Proc. SPIE 5753, 1066, 2005). SEMATECH has set an outgassing limit of 6.5E+14 molecules/cm2/sec for resists that can be used in the currently available prototype EUV tools (K. R. Dean et al., Proc. SPIE, 6519, 65191P-1, 2006). When high volume manufacturing (HVM) tools become available, the limiting value is expected to be revised downward. Previous studies also have shown that most of the outgassed species in chemically amplified resists come from the acid-catalyzed cleavage of the protecting groups and the decomposition products of the photo-acid generator (PAG) (M. M. Chauhan and P. J. Nealey, J. Vac. Sci. Technol. B, 18(6), 3402, 2000). Recent reports, however, have suggested that the light hydrocarbons (<˜100 amu) in the outgassed mixture pose a negligible risk to EUV optics (J. Hollenshead et al., J. Vac. Sci. Technol. B 24(1), 64, 2006).
Therefore, it is desirable to control the outgassing of the photoresist polymer as well as the photo-acid generator (PAG) in order to satisfy the outgassing requirements of the resists.
In chemically amplified resists, to achieve higher resolution in the sub-50 nm regime, low activation energy (low Ea) protecting groups are preferred (G. M. Wallraff et al., J. Vac. Sci. Technol. B 22(6), 3479, 2004.). However, it is generally believed that low activation energy protecting groups will give a higher amount of outgassing during exposure. Therefore, acetal and/or ketal protecting groups, considered to be low activation energy protecting groups, are also expected to give higher amount of outgassing. However, in the absence of moisture, acetal and/or ketal protecting groups will not deprotect even in the presence of photo-acid. This has been demonstrated by the investigation of kinetics of deprotection and by outgassing studies done under electron beam and 248 nm exposure conditions in the absence of moisture (G. M. Wallraff et al., J. Vac. Sci. Technol. B 22(6), 3479, 2004.). Acetal and/or ketal resists are not widely used today in the industry because most of them lack storage stability.